The invention relates to the field of surface measurement and, more specifically, to the field of non-contact surface measurement.
Dimensional metrology, the measurement of the size and shape of objects, is very important in today""s manufacturing environment in which machines perform much of the fabrication and assembly of complex objects composed of many subassemblies. The shape and size of each component in a complex assembly, such as an automobile, must be held to close tolerances to ensure that the components fit together properly.
Ideally such measurements of shape and size are accomplished without physical contact in order to save time in making the measurement. Many non-contact measurement methods make use of available machine vision systems. The measurement of surface contour information is an especially difficult problem in machine vision systems since depth information is often lost or is difficult to interpret. To compensate for the loss of depth information and the difficulty in interpreting the information which is available, many machine vision systems utilize light to create moire patterns on the surface of the object in order to obtain contour information. One disadvantage of the moirxc3xa9 technique is its inflexibility with respect to objects of different sizes. Objects of different sizes may require new corresponding physical setups. Due to this disadvantage, it is difficult to use a moire technique for large-scale objects. Another disadvantage of a moirxc3xa9 technique is that the resolution obtained using the technique may not be high enough for many applications
Interferometric methods have also been used when detailed measurements of the surface are needed. Although interferometric systems provide surface contour information, they are sensitive to vibrations in both the object being measured and the source of illumination being used.
What is needed is a technique which avoids these problems by resolving fringe order ambiguities, mitigating degradation due to speckle effects and attaining high resolution.
The invention is related to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of providing two sources of radiation having a spatial distribution of spectral regions, illuminating the surface with radiation from each of the sources to produce a first fringe pattern at a first position on the surface, moving the first fringe pattern to a second position, generating a first wrapped cycle map in response to the first and second positions of the first fringe pattern, estimating fringe numbers in the first fringe pattern, changing the first fringe pattern to generate a second fringe pattern at a first position, moving the second fringe pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second fringe pattern, estimating fringe numbers in the second fringe pattern in response to the estimated fringe numbers in the first fringe pattern, and determining three-dimensional position information of the point on the surface in response to the estimated fringe numbers in the second fringe pattern and the second wrapped cycle map.
The invention is further related to a method for synthesizing a wrapped cycle map corresponding to a fringe pattern of a predetermined spacing on a surface including the steps of providing two sources of radiation having a spatial distribution of spectral regions, illuminating the surface with radiation from each of the sources to produce a first fringe pattern at a first position on the surface, moving the first fringe pattern to a second position on the surface, generating a first wrapped cycle map in response to the first and second positions of the first fringe pattern, changing the first fringe pattern to generate a second fringe pattern at a first position, moving the second fringe pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second fringe pattern, subtracting the second wrapped cycle map from the first wrapped cycle map, and wrapping the difference between the second wrapped cycle map and the first wrapped cycle map to generate a wrapped cycle map corresponding to the fringe pattern of the predetermined spacing.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of generating a first and a second beam of radiation having a first frequency and being coherent with respect to one another, illuminating the surface with the second beam of radiation, generating a first interference pattern at a first position in response to the first beam of radiation and radiation from the second beam of radiation scattered by the surface, moving the first interference pattern to a second position, generating a first wrapped cycle map in response to the first and second positions of the first interference pattern, estimating intensity cycles in the first interference pattern, changing the first interference pattern to generate a second interference pattern at a first position, moving the second interference pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second interference pattern, estimating intensity cycles in the second interference pattern in response to estimated intensity cycles in the first interference pattern, and calculating three-dimensional position information in response to the estimated intensity cycles in the second interference pattern and the second wrapped cycle map.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of generating a first and a second beam of radiation being coherent with respect to one another, illuminating the surface with the second beam of radiation, generating a first interference pattern in response to the first beam of radiation and radiation from the second beam of radiation scattered by the surface, phase shifting one of the first and second beams of radiation with respect to the other of the first and second beams of radiation to generate a first phase shifted interference pattern, generating a first wrapped cycle map in response to the first interference pattern and the first phase shifted interference pattern, changing the first interference pattern to generate a second interference pattern, phase shifting one of the first and second beams of radiation with respect to the other of the first and second beams of radiation to generate a second phase shifted interference pattern, generating a second wrapped cycle map in response to the second interference pattern and the second phase shifted interference pattern, subtracting the second wrapped cycle map from the first wrapped cycle map, and wrapping the difference between the second wrapped cycle map and the first wrapped cycle map to generate a wrapped cycle map.
The invention also relates to an apparatus for projecting fringes onto a surface of an object including two sources of radiation having a spectral distribution, a collimator in optical communication with the two sources, the collimator generating two substantially collimated beams of broadband radiation, a diffractive grating in optical communication with the collimator, and a lens in optical communication with the diffractive grating, the lens generating two images of radiation having a spatial distribution of spectral regions.
The invention also relates to a method for projecting fringes onto a surface of an object including the steps of providing two sources of radiation separated by a distance and generating radiation having a spectral distribution, collimating the radiation to generate two substantially collimated beams of radiation, delineating spectral components of the collimated beams of radiation, and generating two images of radiation having a spatial distribution of spectral components.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of projecting a first cyclical pattern to produce a first projected pattern at a first position on the surface, moving the first projected pattern to a second position, generating a first wrapped cycle map in response to the first and second positions of the first projected pattern, estimating cycle numbers in the first projected pattern, changing the first projected pattern to generate a second projected pattern at a first position, moving the second projected pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second projected pattern, estimating cycle numbers in the second projected pattern in response to the estimated cycle numbers in the first projected pattern, and determining the surface in response to the estimated cycle numbers in the second projected pattern and the second wrapped cycle map.
The invention further relates to a method for synthesizing a wrapped cycle map corresponding to a projected cyclical pattern of a predetermined spacing on a surface including the steps of projecting a first cyclical pattern to produce a first projected pattern at a first position on the surface, moving the first projected pattern to a second position on the surface, generating a first wrapped cycle map in response to the first and second positions of the first projected pattern, changing the first projected pattern to generate a second projected pattern at a first position, moving the second projected pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second projected pattern, subtracting the second wrapped cycle map from the first wrapped cycle map, and wrapping the difference between the second wrapped cycle map and the first wrapped cycle map to generate a wrapped cycle map corresponding to the projected cyclical pattern of the predetermined spacing.
The invention further relates to a method for mitigating the effects of speckle on a measurement of a point on a surface of an object including the steps of generating a coherent fringe pattern, projecting the coherent fringe pattern along an optical path onto the surface of the object such that the fringe pattern substantially grazes the surface of the object, and detecting the fringe pattern and the speckle in an image of the surface of the object, where a normal to the surface of the object is substantially orthogonal to the optical path.
The invention further relates to a method for mitigating the effects of speckle on a measurement of a point on a surface of an object including the steps of generating a coherent fringe pattern from two sources of radiation separated by a distance, projecting the coherent fringe pattern onto the surface of the object, detecting the fringe pattern and the speckle in an image of the surface of the object, translating the two sources such that the fringe pattern remains substantially stationary and the speckle changes, detecting the new fringe pattern and the changed speckle in an image of the surface of the object, and determining the fringe pattern substantially without speckle in response to the detected fringe patterns and the change in speckle.
The invention also relates to a method for mitigating the effects of speckle on a measurement of a point on a surface of an object including the steps of generating a coherent fringe pattern from two sources of radiation separated by a distance, projecting the coherent fringe pattern onto the surface of the object, detecting the fringe pattern and the speckle in an image of the surface of the object, translating the object laterally with respect to the two sources of radiation along a path parallel to the equiphase plane of the fringe pattern such that the fringe pattern remains substantially stationary with respect to the surface of the object and the speckle changes, detecting the new fringe pattern and the changed speckle in an image of the surface of the object, and determining the fringe pattern substantially without speckle in response to the detected fringe patterns and the change in speckle.
The invention also relates to a method for mitigating the effects of speckle on a measurement of a point on a surface of an object including the steps of projecting a coherent fringe pattern onto the surface of the object, providing a lens having a transmission function having a gradual transmission drop off at the lens edge, and detecting the fringe pattern in an image of the surface of the object, where the transmission function substantially reduces the speckle influence on the measurement.
The invention also relates to a method for mitigating the effects of speckle on a measurement of a point on a surface of an object including the steps of generating a first fringe pattern from two sources of radiation having a first frequency and separated by a distance, changing the first fringe pattern to generate a second fringe pattern by changing the first frequency to a second frequency, and changing the distance in response to the difference between the first frequency and the second frequency, where the ratio of the distance to the difference between the first frequency and the second frequency is substantially constant.
The invention further relates to a method for projecting fringes onto a surface of an object including the steps of providing two sources of radiation separated by a distance, having a spectral distribution, and being coherent with respect to the other of the sources, illuminating the point on the surface of the object with the radiation from each of the sources, moving one of the sources relative to the other of the sources, and detecting radiation scattered by the point on the surface of the object. In another embodiment of the invention, the step of providing two sources of radiation includes providing an initial beam of radiation having a spectral width, generating a first radiation beam at a first beam angle and a second radiation beam at a second beam angle from the initial beam of radiation, and imaging the first radiation beam and the second radiation beam to form the two sources of radiation.
The invention also relates to an apparatus for projecting fringes onto a surface of an object including two sources of radiation separated by a distance, each source having a spectral distribution, and being coherent with respect to the other of the sources, a control system moving each of the sources relative to the other of the sources, and a detector positioned to receive radiation scattered from the point on the surface of the object. In another embodiment of the invention, the two sources of radiation include, an initial source of a beam of radiation having a spectral width, a beam separator in optical communication with the initial source of a beam of radiation generating a first optical beam and a second optical beam, and an imaging system optically connected to the beam separator. The imaging system generates the two sources of radiation each respective source of radiation corresponding to the first optical beam and the second optical beam, respectively.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of providing two sources of radiation having a spectral distribution and being coherent with respect to the other of the two sources, providing a detector at the point on the surface, illuminating the point on the surface of the object with the radiation from each of the sources, moving each of the sources relative to each other, detecting the radiation at the point on the surface of the object, and calculating position information in response to the movement of the sources and the radiation detected at the point on the surface of the object.
The invention further relates to an apparatus for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including two sources of radiation having a spectral distribution and being coherent with respect to one another, a control system moving each of the sources relative to each other, a detector positioned at the point on the surface of the object to receive radiation illuminating the point on the surface of the object, and a processor receiving signals from the detector, the processor calculating position information of the point on the surface of the object in response to the movement of the sources and the radiation received at the point on the surface of the object.